The invention relates to an implantation system for locking nails used in fracture fixation.
Locking nails for the operative repairs of fractures of tubular bones are widely used. For example, application is described in “The Journal of Trauma” of 1993, Vol. 35 No. 5, p. 772 to 775. Typical for such locking nails is the arrangement of two transverse bores, i.e. cross-bores at one end (the distal end, for instance) and at least one transversal bore on the other end (the proximal end, for instance). Bone screws are guided through the transverse bores, which are screwed in at opposing sides into the cortical substance of the bone. Through this, the locking nail is secured axially and against rotation.
When using such locking nails, the position of the transverse bores or locking holes in the locking nail has to be identified, so that the cortical substance of the bone is drilled from the right place from the outside. To do this, a series of aiming or targeting devices has become known, which conveniently operate with X-rays in order to determine the position of the transverse bores with respect to the aiming device. In this case, the bone is drilled in the proper place with the aid of the aiming device and a so-called drilling or aiming sleeve, so that the bone screws can be screwed in. Known aiming devices are conveniently connected to one end (for example, the proximal end) of the nail. In this way, the correspondence of the locking holes to aiming bores in the aiming device is approximately determined. However, it has to be taken into account that by reason of the bone's curvature and possible rotation of the nail upon it being driven into the bone, the expected position of the locking holes does not coincide with the actual one.
For this reason, it has been difficult to perform an accurate identification of the position of the locking holes only by mechanical procedures.
From WO 01/60272 A1, published Aug. 23, 2001 (U.S. Ser. No. 10/203,492 filed Nov. 15, 2002, which is assigned to the Assignee of the present invention, the teachings of which are incorporated herein by reference), a locking nail is disclosed in which a groove parallel to the nail axis is formed in the nail shaft only in the distal portion in the region of the locking holes. The leading axis of the groove cuts the axis of the bore approximately perpendicularly. In the mentioned document, an aiming device is also described, the aiming arm of which is provided with two aiming bores. The aiming bores are formed in a portion of the aiming arm of the aiming device which is elastically yielding. With the aid of a thin rod-like feeler, the actual position of the nail in the bone is determined with the aid of the locking holes and the groove between them. By turning the nail and by axial displacement it can be detected when the feeler is in the region of a locking hole.
It has been found that this purely mechanical method still poses problems for the surgeon, because he cannot always determine in a sufficiently accurate manner the actual position of the nail by actuating the feeler.